1. Field of the Invention
The present invention relates to laser diode arrays, and more specifically, it relates to the use of micro-machined Si wafers and glass inserts to produce laser diode arrays in a ruggedized, high-average-power, low-cost, self-aligned microlensed assembly.
2. Description of Related Art
Laser diode arrays are used in a wide range of commercial, medical and military applications. These applications include materials processing (soldering, cutting, metal hardening), display technology/graphics, medical imaging (MRI) and surgical procedures (corneal shaping, tissue fusion, dermatology, photodynamic therapy), satellite communication, remote sensing, and inertial fusion confinement/energy. In most solid-state laser applications it is desirable to use laser diode arrays to optically excite, i.e., xe2x80x9cpumpxe2x80x9d the crystal hosts. Diodes offer a narrow band of emission, compactness, high electrical efficiency and higher reliability as compared to flash lamps. Despite these numerous advantages, however, diode-pumped solid-state lasers (DPSSLs) have gained slow market acceptance due to the high cost associated with the laser-diode-array pumps. In addition, higher diode array performance (power/thermal) and better system reliability would enable new architectures and wider deployment of DPSSLs than were previously unattainable.
As laser diodes become capable of attaining higher peak output power, it becomes increasingly important to reject the thermal waste heat to not limit the maximum average-power possible. State-of-the-art near-IR laser diodes may produce up to 150 W of peak power/cm, but due to thermal limitations, are typical restricted to xcx9c50 W (for reliable cw operation). The reliable output power level is determined by the temperature of the laser diode junction, which in turn is governed by the thermal impedance of the heatsink. When the diode junction temperature rises, deleterious effects occur, including the loss of output power (and efficiency), wavelength drift and reduced lifetime. Thus, a low-thermal-impedance heatsink will reduce the cost of a diode array in terms of dollars per Watt (average).
Presently, the microchannel cooling technology provides the most aggressive heatsink (i.e., lowest thermal impedance), wherein each laser bar is water-cooled separately from its neighbors. However, this architecture requires the use of elastomer gaskets to form the water seal between neighboring heatsink packages. For large diode array systems, especially those that are subject to vibration or those that cannot be easily maintained (i.e., airborne), the large number of gaskets poses a liability. Most commercial laser diode array architectures eliminate water seals by utilizing a single self-contained water-cooled heatsink that is bonded to an array of diode bars separated by heat spreaders. Unfortunately, the thermal impedance is significantly higher (xcx9c5xc3x97) compared to microchannel heatsinks because the coolant in these architectures cannot be located proximate to the diode bar. This becomes more problematic as diode bars become longer (cavity length  greater than 2 mm), as this necessitates moving the heat source still farther away from the coolant (this could be mitigated by increasing the diode spacing with the penalty of lowering the irradiance). The result is that commercial diode arrays based on non-microchannel-cooled-heatsink technology do not scale well to state-of-the-art diodes under high-average power conditions.
The present invention maintains the maximum possible thermal performance of the microchannel design, while benefiting from an inherently ruggedized architecture that exploits the robustness and simplicity of the more conventional approaches. Moreover, the use of Si micro-machined heatsinks allows a convenient method for fabricating the lens frame within the heatsink itself, which will enable passive lens alignment and further simplify and reduce cost.
It is an object of the present invention to provide a ruggedized, optically corrected, self-aligned, microchannel cooled, laser diode array.
The invention is a 2-dimensional laser diode array having a geometry that combines advanced packaging entities, (e.g., corrective micro-lens, high optical power density and high thermal performance heatsink). Nominal laser diode densities to xcx9c10 bars/cm, that is independent of cavity length (and application), are achieved, which is comparable to or better than other architectures. This design provides the passive alignment of microlenses, which is necessary for simplicity and low cost.
The present laser diode array is rugged and is actively cooled for very-low thermal impedance. The laser diode array of the present invention need not be microlensed for certain applications, may be operated in any pulse-format, and is especially attractive for high-average power or continuous-wave operation, depending on the application. Each laser bar is individually heat sunk by a microchannel layer, even though the manufacturing method of mounting bars is robust and processed at a xe2x80x9cmonolithicxe2x80x9d level. The laser diodes are placed in an array of slots that are accurately placed on the cooler surface and the laser diode emitting surface is placed in close proximity to the edge of the heatsink. The heatsink surface also provides a v-shaped frame that will allow passive or active alignment of microlenses.